Cutting fluid application for titanium alloys Ti-6Al-4V and Ti-10V-2Fe-3Al in a finish turning process

Superalloys such as titanium alloys are classified as hard to machine. Cutting tools and cutting fluids (coolants) are under constant development to improve the machining of such alloys. Coolants remove heat and metal cuttings (chips) from the cutting zone and provide lubrication. Usage of coolant mitigates certain health and safety considerations whilst creating others. Prolonged exposure to coolant fluid and mist can cause health issues. Alternatively, the ignition of dry titanium chips can cause a fire. These risks must be mitigated. For this paper titanium alloys Ti-6Al-4V and Ti-10V-2Fe-3Al were machined, studying the effect of three coolant application conditions in finish turning. The conditions were through-tool delivery of emulsion coolant at 60 bar pressure (known as TT), flood delivery of emulsion coolant and cutting dry with no coolant

Tool wear tests assessed the surface speed at which 15 minutes' tool life could be achieved. It was found that dry turning could be run at between 70 and 80 percent of the speed achieved for TT. The flood condition could achieve 88 to 92 percent of the speed achieved for TT. Dry cutting performed well regarding tool wear, considering the reduction of resource usage and reduced environmental impact. A weakness of dry and flood turning was that chips formed problematic tangled structures.

Individual turned Ti-10V-2Fe-3Al samples had their microstructure analysed. For a sample machined under dry conditions some sub-surface damage metrics were worsened whilst other were improved, compared to samples turned using coolant. No evidence was seen of a burned surface. Recommendations for future work include taking more samples for microstructure analysis.